1. Field of the Invention
The present invention relates to the improvement of the light measurement compensation apparatus for the single lens reflex camera.
2. Description of the Prior Art
Generally, in the case of the so-called TTL totally opened light measuring system in accordance with which the light beam having passed through the photographing lens is directed to the light sensing element so as to measure the light amount, the object brightness BV can be calculated from the totally opened aperture compensation value AVo (F No. of the lens) and the aperture compensation value AVc and brightness BVo measured on the surface of the light sensing element as follows: EQU BV=BVo+(AVo+AVc).
Until now, there are two systems for calculating the object brightness from the above relation, namely, the one in accordance with which the totally opened aperture compensation value AVo and the aperture compensation value AVc are obtained independently and the other in accordance with which the aperture compensation value AVc is written in the ROM and so on. This is done while the totally opened compensation value AVo is read out from the totally opened aperture compensation signal pin of the photographing lens so as to read out the aperture compensation value AVc corresponding thereto.
In the case of one of the conventional two systems, in accordance with which the aperture compensation value AVc and the totally opened aperture compensation value AVo are obtained independently from each other, for one signal pin of the lens two variable resistances, namely, the one for the aperture compensation and the other for the totally opened aperture compensation are mechanically engaged. Thus, it is necessary to provide two systems for the engaging mechanism, which necessarily becomes complicated, while it is also necessary to carry out the adjustment in such a manner that the two systems for the engaging mechanism assume a certain determined relation with each other. This causes the decrease of fidelity by adjustment and the increase of manufacturing cost, which is disadvantageous. Further, the case of the system in which the second ROM and so on are used, the calculation circuit becomes complicated and, therefore, it is difficult to cut the manufacturing cost, which is disadvantageous.